The invention concerns a method for the production of a nuclear magnetic resonance (NMR) tomography image with radio frequency (RF) signals from an extended measuring object being detected by n surface coils of an NMR apparatus, whereby n&gt;1, and the n RF signals are separately preamplified by n preamplifiers each assigned to one of the n surface coils, and subsequently further amplified and detected in a phase sensitive fashion, as a result of which a low frequency signal is obtained in each case which is introduced to one of n low pass filters of an analog/digital converter (ADC) and whereby n partial images are produced in a computer from the n signals obtained in this fashion and assembled into a single NMR tomography image of the measuring object in a region of interest.
A method of this type is known in the art, for example, from EP 0 472 390 A2.
With NMR tomography high field magnets, having increasing magnetic field strengths, it is an ever increasing problem to construct functioning surface coils with sufficient FOV (field of view). This is the case for medical applications in particular with spatially extended organs, such as the human spine. The reason for this is that this type of large area coil does not have good radio frequency properties, e.g. the signal-to-noise ratio is relatively poor.
A recently practised solution therefor utilizes a "coil array" with a plurality of n partial coils which independently, e.g. mutually decoupled, receive signals from the FOV which are separately handled in n individual channel chains and processed via individual ADC's into partial images instead of utilizing one single large coil with one single signal processing chain.
The advantage of the n-chain solution over the classical 1-chain configuration is that each of the n partial coils exhibits a substantially larger Q-factor due to their resulting smaller dimensions.
This type of n-chain configuration is, for example, described in the patent manuscripts U.S. Pat. No. 4,871,969 or U.S. Pat. No. 5,144,243.
A substantial disadvantage in the configuration known in the art consists in the immense hardware costs and problems, since in addition to the devices for RF amplification, demodulation and filtering, a plurality of expensive high speed ADC's must also be available. Moreover, a special extremely costly and/or difficult interface is necessary to introduce the n signals from the different partial coils into the input of an available standard computer which normally accommodates a conventional 1-chain configuration. In order to be able to transfer the acquired data at all in a reasonable fashion into the computer a structure, which is not initially available, must be created. For these reasons, it is nearly impossible to retroactively reconfigure a tomography system into a multiple chain system for cost and space reasons.
It is therefore the purpose of the present invention to present a method of the above mentioned kind which, despite the utilization of an n-chain configuration, is sufficiently simplified that an easy adaptation to available data processing systems for NMR tomographs is possible, whereby, in comparison to the classical 1-chain configuration, the additional n-1 high speed ADC's which are normally necessary in a multiple chain configuration can be dispensed with.